A Functionally Asymmetric Janus Hygro-Photothermal Hybrid for Atmospheric Water Harvesting in Arid Regions.

Metal-organic frameworks (MOFs) are high-performance adsorbents for atmospheric water harvesting but have poor water-desorption ability, requiring excess energy input to release the trapped water. Addressing this issue, a Janus-structured adsorbent with functional asymmetry is presented. The material exhibits contrasting functionalities on either face - a hygroscopic face interfaced with a photothermal face. Hygroscopic aluminum fumarate MOF and photothermal CuxS layers are in-situ grown on opposite sides of a Cu/Al bimetallic substrate, resulting in a CuxS-Cu/Al-MOF Janus hygro-photothermal hybrid. The two faces serve as independent "factories" for photothermal conversion and water adsorption-desorption respectively, while the interfacing bimetallic layer serves as a "heat conveyor belt" between them. Due to the high porosity and hydrophilicity of the MOF, the hybrid exhibits a water-adsorption capacity of 0.161 g g-1 and a fast adsorption rate (saturation within 52 min) at 30% relative humidity. Thanks to the photothermal CuxS, the hybrid can reach 71.5 °C under 1 Sun in 20 min and desorb 97% adsorbed water in 40 min, exhibiting a high photothermal conversion efficiency of over 90%. CuxS-Cu/Al-MOF exhibits minimal fluctuations after 200 cycles, and its water-generation capacity is 3.21 times that of powdery MOF in 3 h in a self-designed prototype in one cycle.

Bimetallic MOF-Derived Solar-Triggered Monolithic Adsorbent for Enhanced Atmospheric Water Harvesting.

The development of economical, energy-saving, and efficient metal-organic framework (MOF)-based adsorbents for atmospheric water collection is highly imperative for the rapid advancement of renewable freshwater resource exploitation. Herein, a feasible one-step solvothermal formation strategy of bimetallic MOF (BMOF) is proposed and applied to construct a solar-triggered monolithic adsorbent for enhanced atmospheric water collection. Benefiting from the reorganization and adjustment of topology structure by Al atoms and Fe atoms, the resultant BMOF(3) consisting of Al-fumarate and MIL-88A has a higher specific surface area (1202.99 m2  g-1 ) and pore volume (0.51 cm3  g-1 ), thereby outperforming the parental MOFs and other potential MOFs in absorbing water. Expanding upon this finding, the solar-triggered monolithic adsorbent is further developed through a bottom-up assembly of polyaniline/chitosan layers and hybridized BMOF(3) skeletons on a glass fiber support. The resultant monolithic adsorbent exhibits superior sorption-desorption kinetics, leading to directional water transport and rapid solar-assisted vapor diffusion. As a proof-of-concept demonstration, an exquisite water harvester is constructed to emphasize a high water yield of 1.19 g g-1 per day of the designed monolithic adsorbent. Therefore, the design and validation of bimetallic MOF-derived solar-triggered adsorbent in this work are expected to provide a reference for the large-scale applications of MOF-based atmospheric water harvesting.

Noncell-autonomous HSC70.1 chaperone displays homeostatic feedback regulation by binding its own mRNA.

The HSC70/HSP70 family of heat shock proteins are evolutionarily conserved chaperones involved in protein folding, protein transport, and RNA binding. Arabidopsis HSC70 chaperones are thought to act as housekeeping chaperones and as such are involved in many growth-related pathways. Whether Arabidopsis HSC70 binds RNA and whether this interaction is functional has remained an open question. We provide evidence that the HSC70.1 chaperone binds its own mRNA via its C-terminal short variable region (SVR) and inhibits its own translation. The SVR encoding mRNA region is necessary for HSC70.1 transcript mobility to distant tissues and that HSC70.1 transcript and not protein mobility is required to rescue root growth and flowering time of hsc70 mutants. We propose that this negative protein-transcript feedback loop may establish an on-demand chaperone pool that allows for a rapid response to stress. In summary, our data suggest that the Arabidopsis HSC70.1 chaperone can form a complex with its own transcript to regulate its translation and that both protein and transcript can act in a noncell-autonomous manner, potentially maintaining chaperone homeostasis between tissues.

Crosstalk between heat shock factor 1 and signal transducer and activator of transcription 3 mediated by interleukin-8 autocrine signaling maintains the cancer stem cell phenotype in liver cancer.

BACKGROUND AND AIM: Liver cancer stem cells (LCSCs) cause therapeutic refractoriness and relapse in hepatocellular carcinoma. Heat shock factor 1 (HSF1) plays versatile roles in multiple cancers. However, the role of HSF1 in LCSCs is not well understood. This study investigated the function and signal mechanisms of HSF1 in maintaining LCSC phenotypes. METHODS: We established two LCSC lines, HepG2-R and HuH-7-R. Constitutive activation of HSF1 was observed in these LCSCs. Specific short hairpin RNAs (shRNAs) and chemical inhibitors were used to identify the relationship between HSF1 expression and LCSCs phenotypes. RESULTS: We revealed a concomitant activation modality involving HSF1 and STAT3 in LCSCs and liver cancer tissues. We also found that liver cancer patients whose HSF1 and STAT3 mRNA expression levels were high presented with unfavorable clinicopathological characteristics. Moreover, the secretion of interleukin-8 (IL-8) was elevated in the LCSC medium and was directly regulated by HSF1 at the transcriptional level. In turn, IL-8 activated HSF1 and STAT3 signaling, and a neutralizing IL-8 antibody inhibited HSF1 and STAT3 activity, reduced cancer stem cell marker expression, and decreased LCSC microsphere formation. Simultaneous intervention with HSF1 and STAT3 led to synergistically suppressed stemness acquisition and growth suppression in the LCSCs in vivo and in vitro. CONCLUSIONS: Our study indicates that IL-8 mediates the crosstalk between the HSF1 and Stat3 signaling pathways in LCSCs and that the combined targeting of HSF1 and STAT3 is a promising treatment strategy for patients with advanced liver cancer.

Academician Wen-Rui Hu - Eminent Pioneer and Prominent Leader of Microgravity Science in China.

In 2021, the scientific community celebrated the 85th anniversary of the Chinese scientist Academician Wen-Rui Hu. In addition to his innovative contributions to cosmic magnetohydrodynamics (MHD) during his early scientific career, he has initiated microgravity science research in China from the middle of 1980s, and made many pioneering contributions to microgravity fluid physics. He has also promoted researches in China in the fields of space material science, space biotechnology, space fundamental physics, and relevant applications. He is respected as the founder of microgravity science in China because of his eminent pioneering contributions and prominent leadership. This article tries to provide a brief historical perspective of the tireless explorations of Academician Wen-Rui Hu in the field of microgravity science and other relevant disciplines till today based on personal views of his former students and colleagues.

Transcriptional Regulation of the Immune Receptor FLS2 Controls the Ontogeny of Plant Innate Immunity.

Innate immunity plays a vital role in protecting plants and animals from pathogen infections. Immunity varies with age in both animals and plants. However, little is known about the ontogeny of plant innate immunity during seedling development. We report here that the Arabidopsis (Arabidopsis thaliana) microRNA miR172b regulates the transcription of the immune receptor gene FLAGELLIN-SENSING2 (FLS2) through TARGET OF EAT1 (TOE1) and TOE2, which directly bind to the FLS2 promoter and inhibit its activity. The level of miR172b is very low in the early stage of seedling development but increases over time, which results in decreased TOE1/2 protein accumulation and, consequently, increased FLS2 transcription and the ontogeny of FLS2-mediated immunity during seedling development. Our study reveals a role for the miR172b-TOE1/2 module in regulating plant innate immunity and elucidates a regulatory mechanism underlying the ontogeny of plant innate immunity.plantcell;30/11/2779/FX1F1fx1.

MiR172b-TOE1/2 module regulates plant innate immunity in an age-dependent manner.

Plant innate immunity varies with age and plant developmental stages. Recently, we reported that Arabidopsis thaliana microRNA miR172b regulates FLS2 transcription through two transcription factors: TARGET OF EAT1 (TOE1) and TOE2. Although the flg22-triggered immune responses were investigated in 2-d-old or even younger toe1/toe2 mutant and miR172b over expression (OE) transgenic plants, the FLS2-mediated immune responses in older plants remain uncharacterized yet. In this work, we analyzed the flg22-triggered immune response in 6-d-old toe1/toe2 and miR172b OE plants. We found that unlike 2-d-old plants, 6-d-old Col-0, toe1/toe2 and miR172b OE plants exhibit comparable flg22-triggered immune responses. Strikingly, miR172b precursor in 6-d-old Col-0 plants upon flg22 treatment reached to a very high level, consequently, the TOE1/2 protein level under this condition was very low or almost undetectable, which explains why 6-d-old WT seedlings are very similar to toe1/toe2 seedlings or miR172b OE plants with respect to the flg22-triggered immune responses. Taken together, our study reveals that miR172b-TOE1/2 module regulates plant innate immunity in an age-dependent manner.

Identification of critical cysteine sites in brassinosteroid-insensitive 1 and novel signaling regulators using a transient expression system.

The plant hormones brassinosteroids (BRs) modulate plant growth and development. Cysteine (Cys) residues located in the extracellular domain of a protein are of importance for protein structure by forming disulfide bonds. To date, the systematic study of the functional significance of Cys residues in BR-insensitive 1 (BRI1) is still lacking. We used brassinolide-induced exogenous bri1-EMS-Suppressor 1 (BES1) dephosphorylation in Arabidopsis thaliana protoplasts as a readout, took advantage of the dramatic decrease of BRI1 protein levels during protoplast isolation, and of the strong phosphorylation of BES1 by BR-insensitive 2 (BIN2) in protoplasts, and developed a protoplast transient system to identify critical Cys sites in BRI1. Using this system, we identified a set of critical Cys sites in BRI1, as substitution of these Cys residues with alanine residues greatly compromised the function of BRI1. Moreover, we identified two negative regulators of BR signaling, pattern-triggered immunity compromised RLCK1 (PCRK1) and PCRK2, that were previously known to positively regulate innate immunity signaling. This work not only provides insight into the functional importance of critical Cys residues in stabilizing the superhelical conformation of BRI1-leucine-rich-repeat, but also reveals that PCRK1/2 can inversely modulate BR and plant immune signaling pathways.

The RCC1 family protein SAB1 negatively regulates ABI5 through multidimensional mechanisms during postgermination in Arabidopsis.

Abscisic acid-insensitive 5 (ABI5) is an essential and conserved plant basic leucine zipper transcription factor whose level controls seed germination and postgerminative development. It has been demonstrated that activity of ABI5 is transcriptionally and post-translationally regulated. However, transcriptional regulation of ABI5 is not fully understood. Here, we identified SAB1 (Sensitive to ABA 1) as a novel negative regulator of ABI5 that simultaneously regulates its stability, promoter binding activity and histone methylation-mediated gene silencing of ABI5. SAB1 encodes a Regulator of Chromatin Condensation 1 (RCC1) family protein and is expressed in an opposite pattern to that of ABI5 during early seedling growth in response to abscisic acid (ABA). SAB1 mutation results in enhanced ABA sensitivity and acts upstream of ABI5. SAB1 physically interacts with ABI5 at phosphoamino acid Ser-145, and reduces the phosphorylation of ABI5 and the protein stability. SAB1 reduces ABI5 binding activity to its own promoter, leading to reduced transcriptional level of ABI5. SAB1 inactivates ABI5 transcription by increasing the level of histone H3K27me2 in the ABI5 promoter. Our findings have identified SAB1 as a crucial new component of ABA signaling which modulates early development of plant by precisely controlling ABI5 activity through multiple mechanisms.

The Arabidopsis RCC1 Family Protein TCF1 Regulates Freezing Tolerance and Cold Acclimation through Modulating Lignin Biosynthesis.

Cell water permeability and cell wall properties are critical to survival of plant cells during freezing, however the underlying molecular mechanisms remain elusive. Here, we report that a specifically cold-induced nuclear protein, Tolerant to Chilling and Freezing 1 (TCF1), interacts with histones H3 and H4 and associates with chromatin containing a target gene, blue-copper-binding protein (BCB), encoding a glycosylphosphatidylinositol-anchored protein that regulates lignin biosynthesis. Loss of TCF1 function leads to reduced BCB transcription through affecting H3K4me2 and H3K27me3 levels within the BCB gene, resulting in reduced lignin content and enhanced freezing tolerance. Furthermore, plants with knocked-down BCB expression (amiRNA-BCB) under cold acclimation had reduced lignin accumulation and increased freezing tolerance. The pal1pal2 double mutant (lignin content reduced by 30% compared with WT) also showed the freezing tolerant phenotype, and TCF1 and BCB act upstream of PALs to regulate lignin content. In addition, TCF1 acts independently of the CBF (C-repeat binding factor) pathway. Our findings delineate a novel molecular pathway linking the TCF1-mediated cold-specific transcriptional program to lignin biosynthesis, thus achieving cell wall remodeling with increased freezing tolerance.

PRL1 modulates root stem cell niche activity and meristem size through WOX5 and PLTs in Arabidopsis.

The stem cell niche in the root meristem maintains pluripotent stem cells to ensure a constant supply of cells for root growth. Despite extensive progress, the molecular mechanisms through which root stem cell fates and stem cell niche activity are determined remain largely unknown. In Arabidopsis thaliana, the Pleiotropic Regulatory Locus 1 (PRL1) encodes a WD40-repeat protein subunit of the spliceosome-activating Nineteen Complex (NTC) that plays a role in multiple stress, hormone and developmental signaling pathways. Here, we show that PRL1 is involved in the control of root meristem size and root stem cell niche activity. PRL1 is strongly expressed in the root meristem and its loss of function mutation results in disorganization of the quiescent center (QC), premature stem cell differentiation, aberrant cell division, and reduced root meristem size. Our genetic studies indicate that PRL1 is required for confined expression of the homeodomain transcription factor WOX5 in the QC and acts upstream of the transcription factor PLETHORA (PLT) in modulating stem cell niche activity and root meristem size. These findings define a role for PRL1 as an important determinant of PLT signaling that modulates maintenance of the stem cell niche and root meristem size.

An Arabidopsis homolog of importin ß1 is required for ABA response and drought tolerance.

The import of proteins into the nucleus in response to drought is critical for mediating the reprogramming of gene expression that leads to drought tolerance. However, regulatory mechanisms involved in nuclear protein import remain largely unknown. Here, we have identified an Arabidopsis gene (AtKPNB1) as a homolog of human KPNB1 (importin ß1). AtKPNB1 was expressed in multiple organs, and the protein was localized in the cytoplasm and nucleus. AtKPNB1 was able to facilitate nuclear import of a model protein. Null mutation of AtKPNB1 delayed development under normal growth conditions and increased sensitivity to abscisic acid (ABA) during seed germination and cotyledon development. Inactivation of AtKPNB1 increased stomatal closure in response to ABA, reduced the rate of water loss, and substantially enhanced drought tolerance. AtKPNB1 interacted with several importin α proteins, nucleoporin AtNUP62, and the Arabidopsis Ran proteins. Inactivation of AtKPNB1 did not affect the ABA responsiveness or the expression level or subcellular localization of ABI1, ABI2 or ABI5, key regulators of the ABA signaling pathway. Moreover, phenotypic analysis of epistasis revealed that AtKPNB1 modulates the ABA response and drought tolerance through a pathway that is independent of ABI1 and ABI5. Collectively, our results show that AtKPNB1 is an Arabidopsis importin ß that functions in ABA signaling.

Symbiotic defect-reinforced bimetallic MOF-derived fiber components for solar-assisted atmospheric water collection.

Conversion of atmospheric water to sustainable and clean freshwater resources through MOF-based adsorbent has great potential for the renewable environmental industry. However, its daily water production is hampered by susceptibility to agglomeration, slow water evaporation efficiency, and limited water-harvesting capacity. Herein, a solar-assisted bimetallic MOF (BMOF)-derived fiber component that surmounts these limitations and exhibits both optimized water-collect capacity and short adsorption-desorption period is proposed. The proposed strategy involves utilizing bottom-up interface-induced assembly between carboxylated multi-walled carbon nanotube and hygroscopic BMOF on a multi-ply glass fiber support. The designed BMOF (MIL-100(Fe,Al)-3) skeleton constructed using bimetallic-node defect engineering exhibits a high specific surface area (1,535.28 m2/g) and pore volume (0.76 cm3/g), thereby surpassing the parent MOFs and other reported MOFs in capturing moisture. Benefiting from the hierarchical structure of fiber rods and the solar-driven self-heating interface of photothermal layer, the customized BMOF crystals realize efficient loading and optimized water adsorption-desorption kinetics. As a result, the resultant fiber components achieve six adsorption-desorption cycles per day and an impressive water collection of 1.45 g/g/day under medium-high humidity outdoor conditions. Therefore, this work will provide new ideas for optimizing the daily yield of atmospheric water harvesting techniques.

Heritable transgene-free genome editing in plants by grafting of wild-type shoots to transgenic donor rootstocks.

Generation of stable gene-edited plant lines using clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) requires a lengthy process of outcrossing to eliminate CRISPR-Cas9-associated sequences and produce transgene-free lines. We have addressed this issue by designing fusions of Cas9 and guide RNA transcripts to tRNA-like sequence motifs that move RNAs from transgenic rootstocks to grafted wild-type shoots (scions) and achieve heritable gene editing, as demonstrated in wild-type Arabidopsis thaliana and Brassica rapa. The graft-mobile gene editing system enables the production of transgene-free offspring in one generation without the need for transgene elimination, culture recovery and selection, or use of viral editing vectors. We anticipate that using graft-mobile editing systems for transgene-free plant production may be applied to a wide range of breeding programs and crop plants.

Biological Activity of Optimized Codon Bovine Type III Interferon Expressed in Pichia pastoris.

Type III interferons (IFN-λs) exhibit potent antiviral activity and immunomodulatory effects in specific cells. Nucleotide fragments of the bovine ifn-λ (boifn-λ) gene were synthetized after codon optimization. The boifn-λ gene was then amplified by splicing using overlap extension PCR (SOE PCR), resulting in the serendipitous acquisition of the mutated boIFN-λ3V18M. The recombinant plasmid pPICZαA-boIFN-λ3/λ3V18M was constructed, and the corresponding proteins were expressed in Pichia pastoris with a high-level extracellular soluble form. Dominant expression strains of boIFN-λ3/λ3V18M were selected by Western blot and ELISA and cultured on a large scale, and the recombinant proteins purified by ammonium sulfate precipitation and ion exchange chromatography yielded 1.5g/L and 0.3 g/L, with 85% and 92% purity, respectively. The antiviral activity of boIFN-λ3/λ3V18M exceeded 106 U/mg, and they were neutralized with IFN-λ3 polyclonal antibodies, were susceptible to trypsin, and retained stability within defined pH and temperature ranges. Furthermore, boIFN-λ3/λ3V18M exerted antiproliferative effects on MDBK cells without cytotoxicity at 104 U/mL. Overall, boIFN-λ3 and boIFN-λ3V18M did not differ substantially in biological activity, except for reduced glycosylation of the latter. The development of boIFN-λ3 and comparative evaluation with the mutant provide theoretical insights into the antiviral mechanisms of boIFN-λs and provide material for therapeutic development.

Hydroa vacciniforme-like lymphoproliferative disorder: A clinicopathological, immunohistochemical, and prognostic study of 24 cases in China.

Hydroa vacciniforme-like lymphoproliferative disorder (HV-LPD) is a rare cutaneous disease associated with Epstein-Barr virus infection. We retrospectively analyzed the clinical presentation, histopathological characteristics, and prognostic study of HV-LPD in 24 Chinese patients. All patients presented with recurrent papulovesicular and necrotic eruptions on the face, neck, and extremities, with 11 showing systemic symptoms. Twenty patients were diagnosed with HV-LPD in childhood (age < 18 years) and four in adulthood (age ≥ 18 years). The median age at diagnosis was 8.5 years old (range, 2-50). Histopathology revealed variably dense lymphocyte infiltration throughout the dermis. All cases were strongly positive for CD3 and Epstein-Barr encoding region based on in situ hybridization. Of 18 cases with a T-cell phenotype, 15 harbored monoclonal rearrangements in T-cell receptor (TCR) genes. Four cases with a natural killer cell phenotype carried polyclonal rearrangements in TCR genes. Among 24 patients, eight (33.3%) received chemotherapy, two (8.3%) allogeneic hematopoietic stem cell transplantation, and both are currently alive without disease. The median follow-up period was 24 months (range, 7-120) and 23 patients were available: 15 (62.5%) were alive, and eight (33.3%) had died. Fourteen cases had a relapse of disease and three developed lymphoma within 24 months of diagnosis. The mean survival time of childhood-onset patients was longer than that of adult-onset patients (36.4 vs. 20.8 months). In summary, the wide clinical course and representative presentation of cases in our center reflect the pedigree characteristics of HV-LPD. Allogeneic hematopoietic stem cell transplantation should be a preferred choice for relapse and refractory patients due to the poor effect of chemotherapy. Adult-onset and high serum EBV DNA loads may indicate an increased risk of aggressive disease in patients with HV-LPD.

Tacrolimus and ascomycin inhibit melanoma cell growth, migration and invasion via targeting nuclear factor of activated T-cell 3.

Melanoma is the most malignant form of skin cancer with high metastatic potential. Nuclear factor of activated T-cells (NFATs) are discovered as transcription factors that regulate the expression of proinflammatory cytokines and other genes during the immune response. Among five NFAT members, NFAT3 is exclusively not expressed in immune cells and its role in progression of different types of cancer remains controversial. Our previous study showed that NFAT3 was highly expressed in skin cancer compared with normal skin tissues and critical for melanoma cell survival and tumor growth. Here, we reported that knockdown of NFAT3 expression, as well as treatment with the calcineurin (CaN) inhibitors, tacrolimus (FK506) or ascomycin (FK520) inhibits melanoma cell migration and invasion, and also proliferation and colony formation. Mechanistic studies revealed that FK506 or FK520 blocked the nuclear translocation and reduced the transcriptional activity of NFAT3. These data support that the antimelanoma effect of FK506 and FK520 is partially mediated by inhibiting the oncogenic factor NFAT3, suggesting that therapeutics based on NFAT3 inhibition may be effective in clinical melanoma treatment.

Heat shock factor 4 regulates the expression of HSP25 and alpha B-crystallin by associating with DEXD/H-box RNA helicase UAP56.

Heat shock factor 4 controls the transcription of small heat shock proteins (e.g., HSP25, alpha B-cyrstallin, and r-crystallin), that play important roles in modulating lens proteostasis. However, the molecular mechanism underlying HSF4-mediated transcription is still unclear. Using yeast two hybrid, we found that HSF4 interacts with the ATP-dependent DEXD/H-box RNA helicase UAP56, and their interaction in lens epithelial cell line was further confirmed by GST-pull down assay. UAP56 is a vital regulator of pre-mRNA splicing and mature mRNA nuclear export. The immunofluorescence assay showed that HSF4 and UBA56 co-localize with each other in the nucleus of lens epithelial cells. Ectopic UAP56 upregulated HSF4-controlled HSP25 and alpha B-crystallin proteins expression, while knocking down UAP56 by shRNA reversed it. Moreover, UAP56 interacts with and facilitates the nuclear exportation of HSP25 and alpha B-crystallin mRNA without impacting their total mRNA expression level. In lens tissues, both UAP56 and HSF4 are expressed in the same nucleus of lens fiber cells, and their expression levels are simultaneously reduced with fiber cell maturation. Taken together, these data suggested that UAP56 is a novel regulator of HSF4 and might upregulate HSF4's downstream mRNA maturation and nuclear exportation.

A Novel Cx50 Insert Mutation from a Chinese Congenital Cataract Family Impairs Its Cellular Membrane Localization and Function.

Mutations in GJA8 are associated with hereditary autosomal dominant and recessive cataract formation. In this study, a novel insert mutation in GJA8 was identified in a Chinese congenital cataract family and cosegregated with the disease in this pedigree. This insert mutation introduces five additional amino acid residues YAVHY after histidine at the 95 site (p.H95_A96insYAVHY) within the second transmembrane (TM2) domain of Cx50 protein (Cx50-insert). Ectopic expression of Cx50-insert protein impairs the hemichannel functions and gap junction activity compared to wild-type Cx50 protein in human lens epithelial cells. Cx50-insert proteins were mislocated from cytoplasmic membrane to endoplasmic reticulum and lysosome. In mouse lens tissue, our results showed that Cx50 predominant expresses in epithelial cells and fiber cells at the transition zone of lens hinting its roles in lens differentiation. Taken together, these data suggest that the novel insert mutation in the TM2 domain of Cx50 protein, which impairs its trafficking to the cell membrane and gap-junction function, is associated with the cataract formation in this Chinese pedigree.

Comparative study of Arabidopsis PBS1 and a wheat PBS1 homolog helps understand the mechanism of PBS1 functioning in innate immunity.

Arabidopsis AVRPPHB SUSCEPTIBLE1 (PBS1) serves as a "decoy" in activating RESISTANCE TO PSEUDOMONAS SYRINGAE5 (RPS5) upon cleavage by Pseudomonas phaseolicola B (AvrPphB), a Pseudomonas syringae effector. The SEMPH motif in PBS1 was thought to allow it to be distinguished by RPS5 from the closely related Arabidopsis kinases. However, the underlying mechanism is not fully understood. Here, we isolated and characterized a wheat PBS1 homolog, TaPBS1. Although this plasma membrane-localized kinase could be cleaved by AvrPphB and could associate with RPS5, it failed to trigger RPS5-mediated hypersensitive response (HR) in a transient assay. TaPBS1 harbors a STRPH motif. The association of RPS5 with TaPBS1 was weaker than with PBS1. Change of the STRPH motif to the SEMPH motif allowed TaPBS1 to trigger HR. However, the SEMPH motif is not required for association of PBS1 with RPS5. The difference between "SEMPH" and "STRPH" points to the importance of "EM" in PBS1. Furthermore we found that a negatively charged amino acid at the position of "E" in the SEMPH motif was required for recognition of PBS1 by RPS5. Additionally, both PBS1 and TaPBS1 undergo the flagellin-induced phosphorylation. Therefore, our work will help understand the mechanism of PBS1 functioning in plant innate immunity.